1. Technical Field
The present disclosure relates to a two-cylinder hermetic compressor used for an outdoor unit of an air conditioner and a freezer.
2. Description of the Related Art
Generally, a hermetic compressor used for an outdoor unit of an air conditioner and a freezer includes an electric motor unit and a compressor mechanism unit in a sealed container. The electric motor unit and the compressor mechanism unit are connected to each other by a shaft, and a piston attached to an eccentric portion of the shaft revolves with the rotation of the shaft. A main bearing and an auxiliary bearing are mounted on both end faces of a cylinder having the piston provided therein, and the shaft is supported by the main bearing and the auxiliary bearing. In most cases, the diameter of the shaft is constant except for an eccentric portion.
On the other hand, PTL 1 (Unexamined Japanese Patent Publication No. 2008-14150) discloses a shaft having different diameters.
In PTL 1, the side on which the electric motor unit is provided with respect to the eccentric portion is defined as a main shaft portion, and the side opposite to the side on which the electric motor unit is provided is defined as an auxiliary shaft portion, wherein the diameter of the auxiliary shaft portion is set smaller than the diameter of the main shaft portion.
Note that, in PTL 1, a thrust load of the shaft is received by the lower end of the auxiliary shaft portion, except for the case in which a rolling bearing is provided on an auxiliary bearing.
Meanwhile, in a one-cylinder hermetic compressor that has conventionally been used most often, stress exerted from a compression chamber is received by a main shaft portion disposed on the side of an electric motor unit, so that stress received by an auxiliary shaft portion is extremely small.
Therefore, even if the diameter of the auxiliary shaft portion is set smaller than the diameter of the main shaft portion as disclosed in PTL 1, any problems hardly occur.
However, it has been shown as a result of an analysis that, in a two-cylinder hermetic compressor, stress exerted from each of compression chambers is dispersed into the main shaft portion and the auxiliary shaft portion, so that large stress is also applied on the auxiliary shaft portion.